APPENDIX A 



At Ssumao, Tali-Fou, and Atentse I was able to compare my altitudes with those 

 given by other travellers, with the subjoined satisfactory result : — 



Feet. Feet. 



Ssumao . . . 4,568 . . . 4.542 (Francis Gamier). 



„ ,. ,, ( 6,078 (Francis Gamier). 



Tali-rou . . . 7,007 . . • ■ /T. V. V 



" ' ( 7)07° (Baber). 



Atents^ . . . 11,060 . . . 1 1,000 (Captain Gill). 



II. Column 2 gives the temperature at the moment of the observation, taken 

 with a sling thermometer of Baudin's. 



III. Columns 3 and 4 contain the mean barometric pressure and temperature 

 at sea-level on the same date as the observation. I selected Hong-Kong, Amoy, 

 and Shanghai for base, according as our route lay nearest to their respective latitudes. 

 The readings were kindly furnished by M. Bourgeois, chancellor of the French 

 Consulate at Hong-Kong, who caused the daily meteorological bulletins of the coast 

 of China from February to October to be forwarded to Paris ; after ist October I 

 received only the monthly mean. 



IV. In column 5 will be found the degree of latitude nearest to the place of 

 observation which enters into the calculations for the correction of temperature. 



V. Lastly, column 6 gives the altitudes calculated after the Radau Tables based 

 on the formula of Laplace. The readings at the point of observation enter simul- 

 taneously into the calculation with the corresponding ones under the same parallel 

 by the seashore. They are not laid down as correct to a foot, because one cannot be 

 sure of the local variations in pressure being identical at Hong-Kong and in Yiinnan ; 

 but, speaking generally, the monthly changes follow the same laws of increase and 

 decrease, — maximum pressure in January, minimum in July, — the amplitude reaching 

 the mean figure of .59055 inch, about 492 feet. Besides that this is the method most 

 universally employed by travellers, it must be owned that one has no better base at 

 one's disposal for disengaging the absolute altitude from the observed pressure. The 

 process of calculation being clearly set forth in the preface to the Radau Tables (Paris, 

 Gauthier-MUars), I abstain from reproducing it here. 



P.\RIS, \llh June 1896. 



V. REMARKS ON THE METHODS USED FOR FIXING THE 

 PRINCIPAL POSITIONS ON THE MAP 



I. Manhao (point of departure) 



Latitude = 23° 00' 30" N. Astronomical observations. 



Longitude = 100° 54' E. F'ollowing the map of the staff, 1/200,000, published 

 by the Topographic Service of Hanoi (page Mongtse), showing the labours of the 

 Frontier Delimitation Commission. 



2. S.SU.\IAO 



Latitude = 22° 46' 30" N. Astronomical observations. 



Longitude = 98° 42' 30" E. This longitude is the mean of the three following : — 

 (i) That given by my estimated distance: 98' 37'. 



(2) That given by my astronomical observations : 98° 47' 30". 



(3) That given by Francis Gamier's observations: 98° 43'. 



(F'or the advantage of this mode of adoption, see the observations at the end of 

 the list of longitudes, supra.) 



377 



